<form class="navbar-form form-inline my-2 my-lg-0" method="get" id="searchform" action="<?php echo home_url('/'); ?>">
    <div class="form-group">
        <div class="input-group">
            <input class="form-control navbar-collapse" type="text" placeholder="请输入搜索关键词" name="s">
            <span class="input-group-btn">
                <button class="btn btn-success navbar-collapse" type="submit"><span class="fui-search"></span></button>
            </span>
        </div>
    </div>
</form>